Why DOES prop_static require special model files?

I've never understood this. Some props aren't eligible to be used as static props because they weren't compiled with a specific line of code. And this feels totally arbitrary. Static props don't contain any data that dynamic props don't. All they need is the mesh. Not even a collision mesh if you don't want to use one. It's like there's a single line of code in the compiler that's like "does this prop_static have this particular bit set to 1? If not, then refuse to include it because I said so". Like that one bit of code that prevents Halo 2 from running on anything other than Vista.

This just frustrates me because there are a number of stock props that were not compiled with the $static parameter, also seemingly for no reason whatsoever, that people occasionally want to be able to use as such.